Effects of Hypoxia on the Ventral Root Motor-Evoked Potential in the In Vitro Spinal Cord Preparation

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Abstract
This study investigated the effects of hypoxia and glucose on motor functions of spinal cord, monitoring ventral root motor-evoked potential in the in vitro cervical cord preparations. To study ischemia-induced changes in ventral root motor-evoked potential of spinal cord. Previous studies demonstrated ischemic changes caused by local circulatory impairment might be a major pathophysiologic basis of neuron damage in cord compression. Ventral root motor-evoked potential elicited by stimulation of ventrolateral funiculus was recorded from the ventral root in the isolated spinal cord preparations obtained from a newborn rat. The preparations were exposed to artificial cerebrospinal fluid equilibrated with severe or mild hypoxia for 90 minutes. Inhibitory and excitatory neurotransmitter antagonists were added to artificial cerebrospinal fluid to investigate synaptic transmission. The artificial cerebrospinal fluids containing various concentrations of glucose were used to study the glucose's effects. Ventral root motor-evoked potential consisted of the early and late components, which were excitatory transsynaptic potentials. The amplitudes were increased in the early phase of severe hypoxia and declined in the prolonged exposure. In mild hypoxia, there was a sustained increase of the amplitudes. The application of inhibitory neurotransmitter antagonists abolished the augmentation of the amplitudes in the early phase of severe hypoxia. Hypoxia without glucose accelerated hypoxic change. Inhibitory synaptic transmission was depressed preferentially in the early phase of severe hypoxia or in mild hypoxia. Excitatory and inhibitory transmissions were suppressed in prolonged severe hypoxia. Glucose deficiency aggravated hypoxic inhibition of synaptic transmissions.